This invention relates to an ink jet head which jets ink from a nozzle hole by deforming the partition walls of an ink chamber by a shearing force and to the method of manufacturing the ink jet head.
As a letter printing apparatus by the ink jet method of a drop-on-demand type using the shear deformation mode, there is one that jets ink in an ink chamber from a nozzle hole by applying an electric voltage to the electrodes to deform the partition walls partitioning the ink chamber by a shearing force.
In a conventional ink jet head of a shear deformation (shear mode) type, the drive electrode for shear-deforming (deforming by a shearing force) the partition wall is usually connected to the outside wiring with a lead wire along the partition wall by utilizing the bending portion formed at the time of working the slot forming the ink chamber. According to this method, it is difficult to lead outside the electrode provided at the inner wall of the ink chamber; hence, a compact design of an ink jet head can not be made.
Further, owing to a long outside-leading wire from the drive electrode provided at the inner wall of the ink chamber made up of a piezoelectric element, an electrostatic capacitance which can not be neglected in comparison with the electrostatic capacitance of the driving electrode portion is produced because of the high dielectric constant of the piezoelectric element, to make the load for driving large. For example, the load for driving becomes 2 to 4 times the load of the actual driving portion; thus, the heat generation during the driving poses a problem, and in particular, it makes an obstacle in the case where a high-speed ink jet printing unit having multiple nozzles is brought into actual use.
This invention has been done in view of the above-described points, and it is an object of the invention to provide an ink jet head which is capable of being driven at a high speed, is capable of making a high-quality image recording, has drive electrodes which are led outside in a simple way and reliably, is of low cost, and has a possibility to be made compact, and the method of manufacturing the same.
In order to solve the above-described problems and to accomplish the object, the structure of this invention has been made as follows:
An ink jet head, comprises:
partition walls made of an piezoelectric material and for dividing ink chambers;
driving electrodes provided on the partition walls, and
lead conductors each of which is provided at a bottom portion of each ink chamber and is connected with a driving circuit, each lead conductor connected with the driving electrodes at the bottom portion of each ink chamber so that a voltage is applied from the driving circuit through the lead conductor to the driving electrodes for each ink chamber, whereby the partition walls are deformed by shearing forces and an ink is jetted from each ink chamber.
Further, the above object may be attained by the following preferable structures.
(1) An ink jet head comprising ink chambers provided in a piezoelectric element and drive electrodes provided on the partition walls partitioning said ink chambers, jetting ink from nozzle holes by applying an electric voltage to said drive electrodes to shear-deform (deform by a shearing force) said partition walls partitioning said ink chambers, wherein said drive electrodes provided on said partition walls are connected to lead conductors from a drive circuit provided at the bottom side of said ink chambers.
According to the invention set forth in the above paragraph (1), the drive electrodes are connected to the lead conductors from the drive circuit provided at the bottom side of the ink chambers, that is, connected to the outside drive circuit at positions directly beneath the driving portions; hence, the electrostatic capacitance owing to the connection can be neglected to generate only a small amount of heat, and drive electrodes can be made light-weighted and small-sized. Thus, a line head with highly integrated nozzles which is capable of being driven at a high speed and is capable of making a high-quality image recording can be actualized, and the power source of the printing unit equipped with the ink jet head can be made small-sized and of small rated power. Further, the outside-leading of the drive electrodes is simple and reliable, to make a small-sized printing unit which is of low cost and compact, works at high speed and records an image of a high definition and high quality.
(2) An ink jet head set forth in the paragraph (1), wherein a print wiring substrate is used for the lead conductors from the aforesaid drive circuit, the aforesaid piezoelectric element is provided on this printed circuit board, the aforesaid ink chambers are formed at positions agreeing with the wiring positions in such a manner as to make the lead conductors exposed, and the aforesaid drive electrodes are connected to the lead conductors at the time of forming said drive electrodes on the partition walls.
According to the invention set forth in the above paragraph (2), the piezoelectric element is provided on the printed circuit board, the ink chambers are formed at the positions agreeing with the wiring positions in such a manner as to make the lead conductors exposed, and the drive electrodes are connected to the lead conductors at the time of forming said drive electrodes on the partition walls; hence, a process such as wire bonding or soldering as is heretofore done is not required, and the connection to the lead conductors from the drive circuit can be made simultaneously at the time of attaching the drive electrodes, to make it possible to omit the wiring process; thus, the outside-leading of the drive electrodes is simple and reliable, to make the ink jet head of low cost and compact.
(3) An ink jet head set forth in the paragraph (2), wherein the aforesaid printed circuit board has through-holes at the positions corresponding to the aforesaid ink chambers, and the aforesaid drive electrodes are connected to the lead conductors provided in these through-holes.
According to the invention set forth in the above paragraph (3), the printed circuit board has through-holes at the positions corresponding to the ink chambers, and the drive electrodes are connected to the lead conductors provided in these through-holes; hence, it is prevented that the wiring pattern of the printed circuit board is shaved off to make a poor connection at the time of working the ink chamber owing to the error in the depth of working.
(4) An ink jet head set forth in the paragraph (2) or (3), wherein the aforesaid printed circuit board is made of a material having a Young""s modulus larger than that of the piezoelectric element.
According to the invention set forth in the above paragraph (4), the printed circuit board is made of a material having a Young""s modulus larger than that of the piezoelectric element; hence, the piezoelectric element can be reliably supported even when the partition walls of the ink chambers are shear-deformed.
(5) An ink jet head set forth in the paragraph (2) or (4), wherein the aforesaid printed circuit board is made of a non-piezoelectric ceramics material.
According to the invention set forth in the above paragraph (5), the printed circuit board is made of a non-piezoelectric ceramics material; hence, the piezoelectric element can be reliably supported even when the partition walls of the ink chambers are shear-deformed.
(6) An ink jet head set forth in the paragraph (5), wherein the aforesaid non-piezoelectric ceramics material is at least any one selected from alumina, aluminum nitride, zirconia, silicon, silicon nitride, silicon carbide, and quartz.
According to the invention set forth in the above paragraph (6), the non-piezoelectric ceramics material is at least any one selected from alumina, aluminum nitride, zirconia, silicon, silicon nitride, silicon carbide, and quartz; hence, the piezoelectric element can be reliably supported.
(7) An ink jet head set forth in any one of the paragraphs (2) to (6), wherein at least the surface of the aforesaid printed circuit board to make the bottom of the ink chambers is a smooth surface.
According to the invention set forth in the above paragraph (7), the surface of the printed circuit board to make the bottom of the ink chambers is a smooth surface; hence, the thickness of the adhesive layer to bond the printed circuit board and the piezoelectric element can be made thin, and the both rigid bodies can be held together, to make the jetting efficiency high.
(8) An ink jet head set forth in any one of the paragraphs (2) to (7), wherein the aforesaid printed circuit board is connected to a drive circuit board which is separately provided to this printed circuit board, and a drive circuit is built on said drive circuit board.
According to the invention set forth in the above paragraph (8), the printed circuit board is connected to a drive circuit board which is separately provided, and a drive circuit is built on said drive circuit board; hence, the ease of operation for attaching the drive circuit is improved and the degree of freedom in designing is enlarged.
(9) An ink jet head set forth in any one of the paragraphs (1) to (7), wherein a drive circuit is built on the aforesaid printed circuit board, and this drive circuit is connected to the aforesaid drive electrodes.
According to the invention set forth in the above paragraph (9), a drive circuit is built on the printed circuit board, and this drive circuit is connected to the aforesaid drive electrodes; hence, the outside-leading of the drive electrodes is simple and reliable, and the ink jet head becomes of low cost and compact.
(10) An ink jet head set forth in any one of the paragraphs (1) to (9), wherein ink supply paths leading to the aforesaid ink chambers are formed in the aforesaid printed circuit board.
According to the invention set forth in the above paragraph (10), ink supply paths leading to the aforesaid ink chambers are formed in the aforesaid printed circuit board; hence, it is easy to make a piping work for supplying ink.
(11) The method of manufacturing an ink jet head comprising the steps of bonding a printed circuit board provided with lead conductors in its through-holes and a piezoelectric element, slightly shaving off the surface of said printed circuit board by working ink chambers from the side of the piezoelectric element after the bonding, making said lead conductors in said through-holes exposed, forming drive electrodes on the inner walls of said ink chambers and connecting them to said lead conductors, and bonding a cover member to said piezoelectric element to close the ink chambers.
According to the invention set forth in the paragraph (11), the electrodes are connected to the outside drive circuit at the positions directly beneath the driving portions; hence, the electrostatic capacitance produced by the connection can be neglected to make the drive power source light-weighted and small-sized, and on top of it, a special connecting process can be omitted because the connection to the lead conductors of the drive circuit can be carried out simultaneously at the time of attaching the drive electrodes. Thus, the ink jet head is capable of being driven at a high speed, is capable of making a high-quality image recording, has drive electrodes which are led outside in a simple way and reliably, is of low cost, and has a possibility to be made compact.